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Slugging Your Mosin-Nagant

March 16, 2016

By Rob Behr

The Mosin-Nagant rifle is one of the last great deals available to the American shooting public. Like most great rifle deals, however, there are a few idiosyncrasies that must be addressed in order to get good value for your money. One of the most common issues is matching the correct bullet to the bore dimension.
Most Russian made (including Soviet era 91/30s) have a groove dimension between .311″ and .313″. Finnish stamped Mosin rifles more commonly have smaller bores more closely aligned with conventional .308 caliber dimensions. A quick look through various loading guides will show that the 7.62X54R is commonly loaded with bullets running from .308″ to .312″, but they will do not explain how to match a rifle to the bullet. The process isn’t very hard.
Slugging the barrel is the first step toward making a Mosin shoot up to its potential. This allows a handloader to match bullet diameter to their individual bore dimension. The necessary items are cheap and easily obtained:
• A .32 caliber lead bullet or similar-sized lead fishing sinker
• Quarter inch wooden dowel (longer than the barrel) cut in three inch lengths
• Good lubricant, like Montana X-Treme Gun Grease
• A mallet or gunsmith’s hammer
Here is the process:

Lube the slug with a good grease

Using one of the dowel pieces as a starter, or a larger wooden dowel, tap the slug into the bore.

Continue to tap in the slug using dowel pieces until it has been pushed completely out of the rifle’s breech.

The slug on the right is the one that was tapped through the barrel.

Using a micrometer or caliper, measure the slug across the grooves which will be the largest dimension on the slug.

In this case, the groove dimension on this rifle was greater than .313, which means it will be better served by .311 caliber bullets like Sierra’s 174 grain match bullet. Hornady’s .312″ 174 grain bullet would also be a good bet. Groove dimensions closer to .3095″ will give better accuracy with .308 caliber bullets.